<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
      console.log('-----------------')
      if (true) {
        console.log('true');
      }
      if (0) {//false
        console.log('0');
      }
      if (!0) {//true
        console.log('!0');
      }
      if ('') {//false
        console.log('空字符串');
      }
      if ('abc') {//true
        console.log('abc');
      }
    </script>
</head>
<body>

</body>
</html>